I find fish oil does wonderful things for my mood and I think helps with the inflamation from arthritis. I also have high cholesterol so it is a triple benefit for me. Not too fond of the fish burps but they don't last too long.
Fish oil has shown some promise as an adjunct to standard mood stabilizers and I took in the past for that purpose as well as other uses as determined by a doctor or psychiatrist. However now that there is the FDA approved medication Lovaza that was developed from fish oil and although developed as an anti-cholesterol medication is used off label for bipolar (there may be other uses as well within a doctor's discretion) that is one that more psychiatrists are wiling to prescribe. I am prescribed Lovaza as a mood stabilizer and it has shown much help and since unlike fish oil its a specific amount that is an FDA approved medication it is safer and also more effective. A doctor could determine whether it would be helpful in any other regard and also the potential interactions with other medications as well as other safety issues.
I haven't tried it myself, but I hear fish oil has an anti-inflammatory effect, particularly for the joints.
It is annoying how NSAIDs react with lithium and such things. I have to be very careful with mixing the pills I take for my period and my valproate. Means lots of pain. Am thinking of trying fish oil soon...